Vacuum pumps are widely used in the servicing of refrigeration circuits as such circuits must be evacuated of air prior to being charged with refrigerant. A variety of commercially available pumps for such purpose are available, such as shown in assignee's U.S. Pat. Nos. 3,791,780; 3,837,764; 3,982,864; 4,295,794 and 4,120,621, and it is known to incorporate multiple pumping stages into such pumps connected in series wherein a high vacuum may be produced. Such pumps use various types of pumping elements, such as pistons, lobes, eccentric rotors, vanes and the like.
In the evacuation of refrigeration circuits, the vacuum pump must handle the lubricant which is used within the circuit to lubricate the compressor, and vacuum pumps usually operate within an oil reservoir for lubrication, sealing and heat dissipation purposes.
An object of the invention is to provide a concise, economical, relatively light weight, rugged, dependable vacuum pump having a long effective wear life and capable of drawing a relatively high vacuum at acceptable pumping capacities particularly suitable for refrigeration servicing purposes.
Another object of the invention is to provide a two stage electrically driven vacuum pump employing outwardly movable vanes within rotors wherein end loading on the second stage rotor is reduced and frictional resistance of rotor rotation is minimized.
Another object of the invention is to provide a two stage vacuum pump using rotor mounted vanes within cylindrical pumping chambers wherein the configuration of the vane tip engaging the chamber is matched to the chamber bore to provide superior compression and gas re-expansion characteristics.
A further object of the invention is to provide a two stage vacuum pump wherein the pumping elements are assembled as a readily replaceable module for ease of assembly and maintenance wherein a pump module can be replaced in the field by relatively inexperienced service personnel.
Another object of the invention is to provide a two stage vacuum pump utilizing rotors each supporting two movable vanes engaging a pumping chamber surface, the rotors being mounted within vane slots which are parallel but radially offset from the associated rotor axis wherein greater displacement is achieved for given rotor and chamber sizes.
An additional object of the invention is to provide a two stage vacuum pump utilizing a pair of rotors mounted upon a common driven shaft, the vanes mounted upon the rotors being rotationally offset with respect to each other about the shaft axis to improve free air capacity and pumping speeds.
In the practice of the invention an electric motor is mounted to a cast pump housing having a handle extending from the upper region thereof wherein the vacuum pump is readily portable and easily handled. Within the pump housing a pump module is located having a shaft in driven relationship with the electric motor shaft, and the housing is partially filled with oil for lubrication, sealing and cooling purposes. The housing is provided with fins to aid in the dissipation of heat.
A pair of cylindrical pumping chambers are defined within the module separated by a center divider valve plate, and a rotor is mounted within each chamber upon the module shaft. The rotors are of a cylindrical form concentric to the associated shaft, and the shaft is eccentrically related to the axis of the pumping chambers. Each rotor includes a pair of parallel slots each intersecting the associated rotor axis, but offset with respect to the rotor axis, and extending toward the rotor circumference in opposite directions intersecting the rotor circumference at diametrical locations.
A flat vane is slidably received within each rotor slot having a tip which engages the associated chamber circumference. The vane tips are matched to the chamber inner diameter, and the rotors are rotationally phased with respect to each other, approximately 20.degree., to improve free air capacity and pumping speed.
Both sides of the second stage rotor are recessed, the associated vane slots communicating with such recesses, and the side of the first stage rotor adjacent the center divider valve plate is also recessed. These recesses interconnect with the crossover porting between the stages and equalizes pressure below all of the vanes which allows the vanes to rapidly seat during start-up, and the recesses also reduce the hydraulic end loading on the second stage rotor, and minimize the friction between the rotors and the module plates.
The end of the pumping module disposed adjacent the pump housing removable end cover plate is closed by a pump face plate having a port communicating with an inlet fitting which is connectable to the refrigeration circuit. The opposite end of the pumping module is enclosed by an exhaust end plate having a valved orifice defined therein whereby the pump's exhaust passes into an exhaust chamber, and through an oil baffle for exhausting through the hollow handle mounted upon the pump housing and the pump can be readily positioned such that the discharge is directed away from the service personnel.